Lap winding is well known as one of methods of winding a stator winding of a rotating electrical machine. In the lap winding, coils adjacent to one another in a circumferential direction of a stator core are wound so that the coils overlap one after another in a radial direction of the stator core and so that an inside and an outside of overlap alternate. In the lap winding method, coils per pole per phase are caused to radially overlap alternately while slots into which the coils are to be inserted are shifted by predetermined pitch. Since a coil is normally made by winding a copper wire at a large number of times, the coil lacks flexibility and has low operability in inserting it into a slot. In view of this drawback, a method has been proposed in which coils per pole per phase are divided into, for example, two groups when to be inserted into slots.
However, when coils divided into two groups are inserted into the slots radially double, this results in differences in the heights of coil ends since crossovers between slots differ between the outer peripheral side and the inner peripheral side. Since parts located at the coil ends do not contribute to the performance of the rotating electrical machine, it is advantageous to reduce the parts located at the coil ends as much as possible.